1. Field of the Invention
The present invention relates to a lighting apparatus for an inspection which is used for irradiating a light on a product to be an inspection object and inspecting the external appearance and scratches of the product, and furthermore, the inspections of the quality of soldering of an electronic components mounted on a substrate in a factory or the like, for example.
2. Prior Art
Examples of the conventional lighting apparatus for an inspection include a coaxial lighting apparatus for coaxially irradiating a light on a CCD camera 7 as shown in FIG. 6, for example. In a casing 21 of a lower end opening type having an upper end provided with an opening 20 for the CCD camera 7, the coaxial lighting apparatus comprises a half mirror 23 having such an attitude as to be inclined by 45 degrees with respect to an optical axis 22 of the CCD camera 7, a large number of light emitting diodes 24 provided facing the lateral side of the half mirror 23 and mounted in the same plane for irradiating a light toward the half mirror 23 in a orthogonal direction to the optical axis 22, and a diffusion plate 25 positioned ahead of the light emitting diode 24. In the case in which an inspection object 4 is for inspection by using the lighting apparatus for an inspection thus constituted, the inspection object 4 is disposed below the lighting apparatus for an inspection. A light emitted from the light emitting diode 24 is diffused by the diffusion plate 25, reflected by the half mirror 23 and thus directed downward, thereby illuminating the inspection object 4. The light applied on and reflected by the inspection object 4 is transmitted through the half mirror 23 and then received by the CCD camera 7 through the opening 20, and the light thus received is subjected to an image processing by an image processing device which is not shown, for example, so that the quality of an image can be determined by a computer.
In the lighting apparatus for an inspection, however, the half mirror 23 having the attitude of a 45-degree inclination is disposed. Therefore, there is a drawback that the size of the whole apparatus is increased in a vertical direction.
Moreover, a space is required for disposing the diffusion plate 25 ahead of the light emitting diode 24. For this reason, there is a drawback that the size of the whole apparatus is also increased in a horizontal direction.
In consideration of the circumstances described above, it is an object of the present invention to provide a lighting apparatus for an inspections which can be reduced in size.
In order to solve the above-mentioned problems, the present invention provides a lighting apparatus for an inspection comprising: lighting means having a large number of light emitters, and guide means including a large number of reflecting portions for reflecting a part of lights emitted from the light emitters and directing the part of lights to an inspection object provided in a lower position, wherein the light for inspection which is applied on and reflected by the inspection object can be received through the apertures among the reflecting portions of the guide member.
Accordingly, by way of circularly disposing the light emitters, consequently, a large number of light emitters can be provided. The light emitted from the light emitters is reflected by the reflecting portion of the guide means, and the light thus reflected is directed to the inspection object provided in a lower position. The inspection object on which the light is irradiated is visually observed through apertures among the reflecting portions of the guide member or an image is picked up by image input means such as a CCD camera to carry out an image processing so that the inspection object can be inspected.
The guide means may be formed of a flat and transparent light guiding plate. Consequently, it is possible to reduce the size of the guiding means in a vertical direction. Moreover, a surface on an opposite side to the inspection object of the light guiding plate is caused to include a dotted pattern with white paint spots or the like grid pattern directly thereon or over a transparent film provided on the surface, or a concavo-convex processing is carried out directly over the surface or over the transparent film provided on the surface, thereby constituting a light diffusing property with the reflecting portion. Consequently, the amount of light irradiation can be uniform in any part of the inspection object. The concavo-convex processing includes embossing capable of forming an emboss pattern having a high concavo-convex degree and graining capable of forming a grain, that is, fine concavo-convex portions such as a so-called wrinkle, pear-skin pattern or the like. A rough surface provided with fine concavo-convex portions is formed by the graining in place of the embossing. Consequently, there is an advantage that the light can be diffused at a small angle, for example, the generation of a glitter in a display screen can be prevented.
By covering the upper surface of the reflecting portion with a layer for absorbing a light, it is possible to avoid such a situation that the light is diffusively reflected by the upper surface of the reflecting portion and recognition is carried out by the image input means with difficulty. While it is preferable that all the lights should be absorbed, it is also possible to permit the case in which all the lights cannot be absorbed but a part of the lights which cannot be absorbed is diffusively reflected.
The light emitting diodes are provided on an outer peripheral edge of the light guiding plate on almost the same level with the light guiding plate in such a state that the top of the light emitting surface is directed toward a central part of the light guiding plate. Consequently, it is possible to dispose a part or all of lighting fields of the light emitting diodes to overlap with the light guiding plate in a horizontal direction. As compared with the case in which the light emitting diodes are provided below the light guiding plate (in a little overlapping position), the size of the lighting apparatus for an inspection can be more reduced in a vertical direction.
Areas of the reflecting portions positioned on a side separated from image input means provided to fetch the light for inspection and to pick up an image are more reduced than those of the other reflecting portions.
For example, in the case in which the reflecting portion having the same area is provided over the whole area of the guide means to pick up an image by a camera to be the image input means, a visual field in the central part of the lens of the camera is darkened and a visual field in an outer peripheral edge portion excluding the central part of the lens becomes bright so that the brightness of the light fetched into the camera is varied depending on the portions of the lens. By setting the areas of the reflecting portions provided apart from the image input means to be smaller than those of the other reflecting portions as described above, consequently, it is possible to cause any portion of the lens to have a visual field having the same brightness. By gradually (stepwise) reducing the area of the reflecting portion from one corresponding to the center of the lens toward the others corresponding to the outer peripheral edge, it is possible to cause the visual field to have the same brightness in all the portions of the lens still more.